Hepatocyte growth factor (HGF) is a pleiotropic cytokine that promotes cell proliferation, motility, survival, and morphogenesis. HGF binds to its receptor c-Met tyrosine kinase and triggers signal transduction that protects cells against apoptosis and enhances cell growth for tissue regeneration. The profound effects of HGF to prevent cell death and to promote tissue regeneration make HGF an interesting drug candidate for therapeutic use. However, the activation of c-Met by HGF also leads to enhanced tumor metastasis and invasion. This pro-invasive feature of HGF has raised concerns regarding its clinical applications. It would be ideal to separate the beneficial cell-protective signals from the pro-invasive signals of HGF. To test this possibility, Michieli et al., (2002) created a recombinant single-chain chimera consisting of a truncated HGF a-chain and a truncated MSP (macrophage-stimulating protein, a cytokine with high homology to HGF) a-chain linked by a short polypeptide linker, termed Metron factor-1 or MF-1. This chimeric HGF-MSP protein can bind to HGF receptor c-Met and MSP receptor Ron independently and elicit a biological signal only through Met-Ron heterodimerization. MF-1 prevents liver or renal damages and enhances liver or kidney regeneration, without inducing tumor metastasis and growth. MF-1 has a short plasma half-life (one hour) and is not suitable for development as therapeutic agent with the common i.v. or s.c. administration route. However, it does provide a unique approach to separate the beneficial organ-protective signaling from undesired pro-invasive signals in HGF-Met pathway. We have designed and constructed a number of novel heterodimeric Fc fusion proteins (trophokines) that can induce Met-Ron heterodimerization. Each of our novel trophokine contains an HGF-Fc and MSP-Fc fusion proteins, which form heterodimers through the knobs-to-holes designed into the CH3 domains of their IgG1 Fc regions. Due to this unique design, each trophokine protein contains one c-Met binding site and one Ron binding site to induce c-Met and Ron heterodimerization. We predict that these newly designed molecules would be able to prevent cell apoptosis and promote tissue regeneration. We also expect elimination of pro-invasive or scattering effects of HGF on cells so that these novel proteins will not promote tumor metastasis or tumor growth. Most importantly, trophokine will have significantly improved plasma half-life and will have easy manufacturing, purification, and other downstream development processes. These novel proteins are likely to provide therapeutic benefit to patients in a wide range of pathological conditions, such as liver cirrhosis, liver fibrosis, renal failure, wound healing, and chemotherapy-induced liver or renal damage. We have successfully expressed four designed trophokine fusion proteins and are currently conducting biochemical and biological characterizations. PUBLIC HEALTH RELEVANCE: Trophokine is a novel protein that can protect tissue damage and promote organ regeneration. Trophokine can provide therapeutic benefit to patients with a wide range of diseases, such as liver cirrhosis and failure, renal failure, pulmonary fibrosis, wound healing, and chemotherapy-induced liver or renal damage. These diseases affect millions of Americans and have unmet needs for new therapies.